1. Field of the Invention
The invention relates to a refrigerator which comprises a freezer compartment, a refrigerating compartment located over the freezer compartment, and a vegetable compartment located below the freezer compartment, and in which cold air is forcedly circulated into these compartments to cool their inner spaces. Moreover, the invention relates to a refrigerator having a damper device for controlling an inflow of cold air to a stock compartment and in which a shape memorizing alloy coil spring is used as a driver for the damper device, and a refrigerator having a defrosting control device for a refrigerator.
2. Description of Conventional Art
Unexamined Japanese Patent Publications (Kokai) HEI-3-267677, HEI-4-103984, and HEI-4-288466 disclose a refrigerator in which a refrigerating compartment is formed over a freezer compartment, and a vegetable compartment below the freezer compartment, and in which cold air cooled by a cooler is circulated into the freezer and refrigerating compartments. In the refrigerator, cold air supplied to the refrigerating compartment is guided to the vegetable compartment through a refrigerating compartment returning passage (feedback passage), and the cold air guided to the vegetable compartment is returned through a vegetable compartment returning passage (feedback passage) to a cooler chamber wherein a cooler is disposed. The refrigerating compartment returning passage (feedback passage) is formed by duct members in the back wall of a heat insulated housing.
A refrigerator of another type is disclosed in Post-examined Japanese Patent Publication (Kokoku) HEI-5-632. In the refrigerator, a stock compartment is divided by a partition into upper and lower compartments, each of the compartments is closed or opened by a drawer type door, and a plurality of containers are held in the stock compartment arranged so as to be vertically arranged and freely movable in the front-to-rear direction. In order to cool the inside of each container, a cold air supplying passage for guiding cold air to the stock compartment is provided with cold air guide ducts each functioning as a cold air passage directed to the corresponding container. In the refrigerator disclosed in the Publication HEI-5-632, one container can be drawn out from one of the stock compartments (in this case, a chilling temperature compartment) which are respectively provided with drawer type doors, by conducting an opening operation on the corresponding door. In a case where one chilling temperature compartment is provided with only one container because of capacity restrictions, there will not particularly arise a problem. In some cases, in the view point of the capacity, food may be stored more efficiently in one compartment when a plurality of containers are arranged in the vertical direction. In such cases, it is required to vertically arrange containers and form cold air guide ducts for respectively guiding cold air to all the containers.
In the refrigerator disclosed in the former three publications, the refrigerating compartment returning passage is located in the back wall (heat insulating material) of the heat insulated housing. In the process of assembling the heat insulated housing, therefore, the work of filling a foamed heat insulating material must be conducted under the state where the duct members are attached to an inner shell. This causes the number of parts including the duct members to be increased, and therefore it is troublesome to mount the duct members to the inner shell. Further, this produces another drawback that it is impossible to exchange the duct members with other ones after conducting the work of filling the foamed heat insulating material. The configuration in which the duct members are embedded in the heat insulating material has drawbacks that the heat insulating property of the back wall of the heat insulated housing is partially degraded, and that dewdrops are produced on the outer shell by heat conduction from the members of the duct through which cold air passes.
On the other hand, in the configuration disclosed in the latter publication wherein a plurality of cold air ducts for guiding cold air to the containers are formed, there arise drawbacks that the existence of the ducts reduces the capacity of the stock compartment, and that the number of parts and the manhour of mounting the ducts are increased as the number of ducts is increased, thereby raising the production cost.
A refrigerator having a freezer compartment and a refrigerating compartment, as mentioned above, is configured so that cold air which is cooled by a cooler in a cooler chamber is sent through a damper device and a cold air duct to the refrigerating compartment to cool its inner space. The damper device is disposed at the inlet of the cold air duct, and operates in such a manner that, when the temperature of the refrigerating compartment is raised to a temperature higher than an upper limit temperature, the opening portion of the damper device is opened to introduce cold air into the cold air duct, and that, when the temperature of the refrigerating compartment is lowered to a lower limit temperature or lower, the opening portion of the damper device is closed to halt the introduction of cold air. As the damper device, useful are dampers such as a gas filled damper thermostat, a motor-driven damper, and a shape memorizing damper which uses as a driver a coil spring of a shape memorizing alloy.
Such a shape memorizing damper is disclosed in, for example, Unexamined Japanese Utility Model Publication (Kokai) HEI-3-7582 and Unexamined Japanese Patent Publication (Kokai) HEI-3-113258. The damper devices disclosed in the publications comprise, as shown in FIG. 18, a damper baffle plate 1101 for opening and closing an opening communicated with a cold air duct through which cold air is sent from a cooler chamber to a refrigerating compartment, and a damper base 1102 which is fixed to the inside of the cold air duct and to which a rotation axis for opening and closing operation of the damper baffle plate is fixed. A heater 1104 is wound on a shape memorizing alloy coil spring 1103 having a helical shape as shown in FIG. 19 and an electrically insulated surface. A DC voltage V.sub.cc (for example, DC 12 V) is applied from a DC power source 1106 to the heater 1104, so that the shape memorizing alloy coil spring 1103 is directly heated by the heater 1104. The shape memorizing alloy coil spring 1103 generates a contraction force due to the shape memorizing effect that, when heated to the austenite phase transition terminate temperature Af (hereinafter, referred to as merely "Af point") or higher, the shape returns to its original one which has been memorized. In FIG. 18, ends of the shape memorizing alloy coil spring 1103 are hooked to the baffle plate 1101 and the damper base 1102, respectively. A bias spring 1105 is hooked to the baffle plate 1101 and the base 1102 in such a manner that the baffle plate is urged in the direction (i.e., the counter direction) opposite to that along which the baffle plate is rotated by the contraction force of the shape memorizing alloy coil spring 1103.
When the refrigerating compartment is to be cooled, the heater 1104 is supplied with a current to heat the shape memorizing alloy coil spring 1103 to the Af point or higher. This causes the shape memorizing alloy coil spring which, at the Af point or higher, has a contraction force greater than the urging force of the bias spring 1105, to contract. By the exerted contraction force, the baffle plate 1101 is lifted up to open the opening of the cold air duct (more specifically, of the damper base). This allows the cold air to enter from the cooler chamber to the refrigerating compartment to cool the inner space of the refrigerating compartment.
In contrast, when the cooling of the refrigerating compartment is to be stopped, the application of the DC voltage V.sub.cc is halted to stop the current supply to the heater 1104 so that the cold air in the vicinity of the damper device cools the shape memorizing alloy coil spring to the martensite phase transition terminate temperature Mf (hereinafter, referred to as merely "Mf point") or lower, thereby canceling or reducing the contraction force of the shape memorizing alloy coil spring. The urging force of the bias spring to pull down the damper baffle plate to close the opening of the cold air duct (more specifically, of the damper base). This causes the introduction of the cold air to be halted, thereby the cooling of the refrigerating compartment is stopped.
In the case where such a shape memorizing damper is to be used in a refrigerator, generally, it is necessary to guarantee that the damper device can operate 100,000 to 300,000 times or more. In other words, a damper device is required to have excellent heat cycle fatigue characteristics and repeating characteristics. Before using in a product, a fatigue test must be conducted under actual service conditions.
When an air blower is operated, moreover, the portion where a damper device is disposed is always exposed to cold air of about -20.degree. to -25.degree. C. Therefore, the following countermeasures are required to be taken. The material of the shape memorizing alloy coil spring is selected so that the lower limit temperature (i.e., the Mf point) for closing the baffle plate by cooling is set to be about -25.degree. C. The quantity of heat applied to the shape memorizing alloy coil spring in order to actuate the baffle plate to the open state is set to be greater than the quantity of cooling attained by the cold air sent by the air blower. The upper limit temperature of the heating in the case of inverse transformation is set so as to be very higher than the preset temperature of the refrigerating compartment (when the Af point is 70.degree. C., for example, the upper limit temperature is set to be 70.degree. C. or higher). As a result of taking these countermeasures, the service temperature range of the shape memorizing alloy coil spring or that of the damper device is from about -25.degree. C. to about 70.degree. C.
In a cooling process wherein the hysteresis is great as shown in FIG. 11, generally, used is a shape memorizing alloy having characteristics in which transformation is conducted in two stages, the intermediate phase (so-called randhedral phase (hereinafter, referred to as merely "R phase"), and the martensite phase (hereinafter, referred to as merely "M phase") (particularly, an combination of an alloy having the R phase and a bias load (bias spring) is used). In this case, the phase transformation proceeds in the sequence of B2.fwdarw. R .fwdarw. M .fwdarw. B2. A specific example of such an alloy which is usually used is a shape memorizing alloy (e.g., a TiNi alloy which does not undergoes an aging treatment) having a temperature zone in which the Af point is 70.degree. C., the austenite phase transition start temperature As (hereinafter, referred to as merely "As point") is 53.degree. C., the martensite phase transition start temperature Ms' in the R phase (referred to as merely "Ms' point") is 55.degree. C., the martensite phase transition terminate temperature Mr' in the R phase (referred to as merely "Mf' point") is 46.degree. C., the martensite phase transition start temperature Ms in the M phase (referred to as merely "Ms point") is 9.degree. C., and the martensite phase transition terminate temperature Mf in the M phase (referred to as merely "Mf point") is in the vicinity of -18.degree. C.
Such a prior art shape memorizing damper has several drawbacks. A first drawback is caused by the operation system of such a damper in which the heater 1104 is supplied with a current in the case of inverse transformation (namely, when the opening is to be opened), and the current supply to the heater 1104 is stopped in the case of transformation (namely, when the opening is to be closed). It is generally recognized in the art that the use of a shape memorizing alloy only in B2 .fwdarw. M and M .fwdarw. Bs transformation impairs the life of the alloy (i.e., the life of the alloy is short) and increases the degree of distortion. Experiments were conducted using such a prior art shape memorizing damper in a refrigerator manufactured by the assignee of the present application. The experimental results show that the stress (contraction force) generated when the shape memorizing alloy was heated to be inversely transformed to the parent phase was remarkably reduced after the operations of opening and closing the damper were repeated several thousands times, as compared with the initial value (the value obtained when the damper was used for the first time).
Next, a second drawback will be described. When a refrigerating compartment is to be cooled, the heater 1104 is supplied with a current to cause the shape memorizing alloy coil spring 1103 to be inversely transformed so that the damper baffle plate 1101 is lifted up by the contraction force due to the inverse transformation. Cold air of about -20.degree. to -25.degree. C. always contacts with the shape memorizing alloy coil spring 1103 and the heater 1104. Therefore, particularly in the heater 1104 which has a small heat capacity, the degree of heat loss is greater than that obtained in the case of windless. Accordingly, the setting of the resistance of the heater and the voltage to be applied to the heater is required to satisfy the condition that the heater generates a considerably large quantity of heat which is sufficient for heating the shape memorizing alloy in the cooled condition to the Af point (e.g., 70.degree. C.) or higher at which the alloy undergoes inverse transformation. This results in that an excessive electric power is necessary as compared with that required in the case of windless. In the view point of power consumption, therefore, such a configuration has a problem in that the power is uselessly consumed. When the cooling of the refrigerating compartment is to be stopped, the current supply to the heater 1104 is stopped to cause the shape memorizing alloy coil spring 1103 to be transformed so that the damper baffle plate 1101 is shut down. In the case where the air blower is operated, the shape memorizing alloy is quickly cooled by circulating cold air, and therefore the damper baffle plate 1101 is rapidly shut down. By contrast, in the case where the air blower is not operated, cold air is not supplied, and therefore it is not possible to quickly cool the shape memorizing alloy, whereby producing a drawback that the damper baffle plate 1101 cannot rapidly be shut down.
Furthermore, in a refrigerator, the amount of frost formed on a cooler generally varies depending on the amount of food in the refrigerator and the frequency of putting food in and out (the frequency approximately equals to the open/close frequency of a door). When frost is formed so as to cover the entire surface of a cooler, the heat exchange capability of the cooler and the quantity of circulating cold air into the refrigerator are reduced. This degrades the cooling power of the refrigerator. For preventing such degradation from occurring, according to a conventional method, the operation of a compressor is stopped at intervals of a predetermined time period, and an electric power is supplied to a defrosting heater, thereby conducting the defrosting.
The defrosting start timing is determined by, for example, a method disclosed in Unexamined Japanese Patent Publication (Kokai) HEI-4-121569. In this method, the open/close frequency of the door is converted into a time period, and the obtained time period is added to the integrated operation time period of a compressor. When the resulting time period reaches or exceeds a certain time period, it is determined to start the defrosting. This method can advantageously prevent a waste defrosting by delaying the defrosting start timing in such a case where, in winter, the operation factor is low, the door is not so frequently opened and closed, and thus frost is not so formed on the cooler. In a defrosting control device disclosed in Postexamined Japanese Patent Publication (Kokoku) SHO-59-38506, the open/close frequency of a door is integrated. When the integrated value reaches a defrosting start value, the defrosting is started. Then, a defrosting start value for the next time is determined on the basis of the time period required for completing the defrosting and the previous integrated value.
In a case where the defrosting start timing is determined only on the basis of the integrated operation time period of the compressor, the defrosting may be started when the door is opened. This makes a user distrustful, and may have a bad influence on the food stored in the refrigerator because of an abnormal temperature rise in the refrigerator which is caused by the fact that the cold air goes out of the refrigerator and the outside air goes into the refrigerator by opening the door, and additionally by the fact that the cooling operation is stopped.
Further, the defrosting timing determination method and the defrosting device disclosed in the above-identified publications have the following drawbacks. In a case where the door is opened and closed at an extremely high frequency, the defrosting may be started even when the compressor has operated only for a short time period. In addition, only the open/close frequency of the door is used as a main factor for determining the defrosting start timing. Accordingly, under an abnormal condition, the defrosting start timing is largely delayed from an appropriate timing, so that the food in the refrigerator goes bad. Such an abnormal condition includes, for example, a case where the humidity of the outside air is very high, a case where the door is opened for a longer time period than that required for putting the food in or out (i.e., the door is left open), and a case where a large amount of food which is not so cold is put in the refrigerator at a time.